1. Field of the Invention
The present invention relates to a recording/reproducing head, a recording/reproducing disk drive and a method for fabricating a magnetic sensor, which are used for a magnetic recording with heating a recording part by light irradiation (Optically Assisted Magnetic (OAM) recording) and reproducing by a magnetic sensor. More particularly, the invention relates to a recording/reproducing head, the recording/reproducing disk drive and a method for fabricating the magnetic sensor, which enable high density recording and high rate data transfer.
2. Description of the Prior Art
For use with hard disk drives (HDD),which perform recording and/or reproducing on magnetic recording films with a magnetic head, magnetoresistive (MR) sensors using magnetoresistance for reproduction or giant-magnetoresistive (GMR) sensors with higher sensitivity and higher resolution (these sensors are collectively referred to as magnetic sensors) have been developed. The recording density has been increased approximately 60% a year in recent years. However, it has turned out recently that the surface density has a limit of approximately 30 Gbits/ (inch)2 because of the super paramagnetic effect: the magnetization direction of a magnetic domain is inverted in the opposite directions by magnetization of adjacent magnetic domains due to thermal disturbance (R. L. White, Tech. Digest of MORIS""99, 11-A-03(1999) P.7).
The optically assisted magnetic (OAM) recording method is proposed as a promising solution to this problem. By this method, the recording is performed by applying magnetic fields and beam spots onto magnetic recording films or magneto-optic recording films and the reproducing is performed with a magnetic sensor such as GMR sensor. The recording is performed with heating a magnetic film by the irradiation of a laser beam for decreasing the magnetization strength of the magnetic films. This method allows recording on a magnetic film of high magnetization, so the magnetization inversion at room temperatures can be avoided. A conventional recording/reproducing disk drives adopting the OAM recording method is described in the literature, xe2x80x9cNikkei Electronics, No. 734, (99.1.11), P.35xe2x80x9d, for example
FIG. 27 shows the recording/reproducing disk drive. The recording/reproducing disk drive 1 has: a semiconductor laser 2 that emits laser beams 3; a polarized beam splitter 33 that separates the laser beam from the semiconductor laser 2 and reflected beam from the recording/reproducing disk 8; a quarter wavelength plate 34 that converts the laser beam 3 from the semiconductor laser 2 to circular polarized beam; a condense lens 4xe2x80x2 that condenses the laser beams 3 from the semiconductor laser 2 after passing through the polarized beam splitter 33 and the quarter wavelength plate 34; a hemispherical solid immersion lens (SIL) 6 that condenses the laser beams 3 from the condense lens 4xe2x80x2, incident from a hemispherical incident surface 6a, to form a beam spot 9a on a beam-condense surface 6c; a flying slider 12 that supports the SIL 6; a coil 10 for modulating magnetic fields, provided in the circumference of the beam spot 9a of the flying slider 12; and a magnetic sensor 11 comprising a GMR sensor.
By the recording/reproducing disk drive 1, the information is recorded in following steps: the semiconductor laser 2 emits a laser beam 3 in a pulse shape; a beam spot 9a is formed on the beam-condense surface 6c of the SIL 6 by the condense lens 4xe2x80x2; a near field wave 9b leaked from the beam-condense surface 6c irradiates a magneto-optic recording film 8b on the recording/reproducing disk 8 to heat the magneto-optic recording film 8b, and at the same time the information is recorded by applying a modulating magnetic field by a coil 10 corresponding to the information. This is referred to as laser-pumped modified field magnetic (LP-MFM) recording. The LP-MFM recording enables recorded mark to be formed shorter than the beam spot diameter. Information is reproduced by scanning the recording/reproducing disk 8 by the magnetic sensor 11 with a magnetic-resistive film used as a detection part. According to the recording/reproducing disk drive 1, since the beam spot 9a can be reduced inversely proportional to the refractive index of the SIL 6, minute magnetic domains of approximately 0.3 xcexcm wide can be formed, so the higher recording density can be achieved.
FIG. 28 shows the above-described LP-MFM recording and the reproduction with the magnetic sensor 11. The LP-MFM recording is performed, as shown in FIG. 28. The laser beam 3, which is turned on and off like a pulse to be adapted to a mark interval. The recording/reproducing disk 8 is moved in the track direction X relative to the magnetic sensor 11. The information is recorded by inverting the direction of applied external magnetic fields corresponding to the basis of recording information. Since circular marks 81 recorded first on a recording track 80 are partially erased due to recording of the next inverted magnetic field, crescent recording marks 81 are formed in the tail of near field wave 9b as shown in FIG. 28. Because the mark length L is determined only by a recording frequency and disk rotation speed, it can be reduced to the size of magnetic particles of the recording film 8b. by increasing the recording frequency.
However, according to the conventional recording/reproducing disk drive 1, the detection part 11a of the magnetic sensor 11 has rectangular shape as shown in FIG. 28. If the crescent marks 81 was scanned with the sensor 11 and the magnetic sensor proceeded to the mark 81 after passing above the central portion of the preceding mark 81, the tail portion of the preceding mark 81 and the present mark 81 would overlapped. So the resolving power would be decreased when the output signal of the magnetic sensor 11 is reproduced on the basis of the reference level S. Further, the output signal of the magnetic sensor 11 is distorted because of the asymmetry between the preceding and following portion of a mark, so the jitter is increased, then the information cannot be correctly reproduced. This phenomenon becomes conspicuous by reducing the mark length L. Although minute recorded mark can be formed during recording, a recording density cannot practically be increased even by use of the LP-MFM recording method because of the limit of the reproducing resolution. The above-mentioned limit of the recording density also limits the transfer rate.
FIG. 29 shows the dependence of the output signals of the magnetic sensor on the mark length L, when the thickness (length in the track direction X) T of the detection part 11a of the magnetic sensor 11 is constant. In this example, the size of a beam spot is 0.2 xcexcm and the length of the detection part 11a of the magnetic sensor 11 is 0.07 xcexcm. As seen from this figure, when the mark length L becomes smaller than the size of the near field wave 9b, output signals is rapidly reduced. Since the jitter is increased at the same time, the reproducible mark length L actually becomes approximately 0.15 xcexcm. Although the shorter marks 81 can be formed by LP-MFM recording and the thickness T of the detection part 11a of the magnetic sensor 11 is thin, these advantages cannot be effectively used.
The present invention provides a recording/reproducing head, a recording/reproducing disk drive which provide a high recording density and a high transfer rate, and a fabrication method of a magnetic sensor used for the head.
The present invention provides a recording/reproducing head, which records recorded mark on recording/reproducing disks by applying magnetic fields and irradiating near field wave and detects magnetic fields from the recorded mark with a magnetic sensor. The head includes a laser beam emitting unit that emits a laser beam, an optical system including a transparent condensing medium having an incident surface on which the laser beam is incident and a condense surface on which the laser beam incident on the incident surface is condensed. The optical system guides the laser beam from the laser beam emitting unit to the incident surface, forms a beam spot by condensing the laser beam on the condense surface, and irradiates the near field wave from the beam spot onto the recording/reproducing disks. The head further includes a magnetic field applying unit, provided near a position where the beam spot is formed, that applies the magnetic fields, and a detection part of the magnetic sensor is almost equal in shape to the recorded mark.
With the above-described configuration, by making the detection part of the magnetic sensor almost equal in shape to the recorded mark, while a signal from one recording mark is being reproduced, signals of the other recorded marks are not picked up, so that resolution is increased. Since an output signal of the magnetic sensor is symmetrical between preceding and following portion and distortion is reduced. The amount of jitter during conversion into a digital signal is reduced, so that information can be correctly reproduced. As a result, a recording density can be increased and a transfer rate is improved more rapidly.
The present invention also provides a recording/reproducing disk drive having the recording/reproducing head described above.
The present invention also provides a recording/reproducing disk drive having plural recording/reproducing disks coaxially disposed at a predetermined interval and plural recording/reproducing heads that record recorded mark on the plural recording/reproducing disks by applying magnetic fields and irradiating near field wave and detect magnetic fields from the recorded mark by a magnetic sensor. Each of the recording/reproducing heads is that described above. The disk drive further has a magnetic field applying unit, provided near a position where the beam spot is formed, that applies the magnetic field, and a detection part of the magnetic sensor is almost equal in shape to the recorded mark.
With the above-described construction, a transfer rate is increased by using plural recording/reproducing heads that perform recording and reproducing on plural recording/reproducing disks.
The present invention also provides a method for fabricating a magnetic sensor that detects magnetic fields from crescent recorded marks having a predetermined curvature, recorded on recording/reproducing disks. The method includes the steps of forming a depression constituting part of a cylindrical surface on a substrate and depositing multi-layer spin valve films on the depression to form a detection part for detecting the magnetic fields, having a curvature almost equal to that of the predetermined curvature.
With the above-described construction, it becomes possible to fabricate a magnetic sensor including a detection part having a curvature almost equal to that of recorded mark.